The Treatment of Combined Posterolateral Knee Injuries and Anterior Cruciate Ligament Tears

Introduction

Posterolateral knee injuries have been noted to be some of the most difficult knee injuries to diagnose and treat due to the multiple different structures, the intricate anatomical relationships, and the fact that there is no one specific clinical test to diagnose these injuries. In addition, the majority of posterolateral knee injuries occur in combination with cruciate ligament injuries and can often be overlooked. Thus it is especially important to always assess for the presence of posterolateral knee injuries whenever a patient presents with an anterior cruciate ligament (ACL) tear.

This chapter will review the surgically relevant anatomy of the posterolateral corner of the knee, the clinical and radiographic diagnosis of these injuries, and the treatment of both acute and chronic combined posterolateral and ACL knee injuries.

Anatomy of the Posterolateral Corner of the Knee

While there have been different defined components of the structures of the posterolateral aspect of the knee, the most important structures are the fibular (lateral) collateral ligament (FCL), popliteus tendon, and popliteofibular ligament (PFL; Fig. 104.1 ). These structures have been defined by biomechanical testing to be the most important to prevent abnormal increases in varus translation, external rotation, and combined coupled posterolateral rotation.

The FCL is the primary stabilizer to varus translation of the knee. It attaches in a small depression just proximal and posterior to the lateral epicondyle and courses distally under the superficial layer of the iliotibial band and the lateral aponeurosis of the long head of the biceps femoris muscle to attach to the lateral aspect of the fibular head. The average length of the FCL has been measured to be 71 mm. Along its more distal quarter, the FCL is located within the confines of the biceps bursa. One of the most important clinical pearls is to identify the FCL by making a horizontal incision in the anterior arm of the long head of the biceps femoris muscle, approximately 1.5 cm proximal to the fibular head, to gain access. Injuries along its distal attachment can be identified here, and a traction stitch placed into the FCL at this location allows for assessment of its integrity and also allows one to follow it proximally to either its avulsed location or its proximal attachment on the femur.

The popliteus tendon is an important primary stabilizer to external rotation and coupled posterolateral rotation of the knee at higher flexion angles. While a true tendon, the popliteus tendon can be considered as the fifth ligament of the knee because it does have some static function, due to it attachment to the fibular styloid, which has been defined by biomechanical testing. Its attachment site is at the anterior fifth of the popliteus sulcus. An important clinical point to recognize is that the distance between the FCL and popliteus tendon femoral attachment site averages 18.5 mm. This anatomical relationship is important to recognize because one graft cannot reconstruct both of these structures due to their differing locations and tensioning patterns with knee flexion, and measuring between the two presumed attachment sites to verify this distance can assist one in finding proper tunnel placement prior to reaming tunnels or for repairing a structure.

The PFL has also been shown to be an important stabilizer to external rotation and a secondary stabilizer to varus opening of the knee. It is a stout structure that connects the popliteus tendon to the posteromedial aspect of the fibular head. The PFL originates at the musculotendinous junction of the popliteus muscle. It courses slightly distal and lateral to attach to the posteromedial aspect of the fibular styloid. It has two divisions, which are called the anterior and posterior divisions. The posterior division is larger and is the division most commonly reconstructed with current techniques.

Diagnosis of Posterolateral Knee Injuries